Foam drive oil recovery process



Sept. 22, 1970 Filed July 24, 1968 2 Sheets-Sheet l G50/@05 6- EPA/400 BY 19M 9AM.

SePt- 22, 1970 G. G. BERNARD 3,529,668

FOAM DRIVE OIL RECOVERY PROCESS Filed July 24, 1968 2 Sheets-Sheet 2 /Q aaa /a A .a/VE 2U/a 645/ Wirf/Q 'f4/va Q :Q S, v

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United States Patent O 3,529,668 FOAM DRIVE OIL RECOVERY PROCESS George G. Bernard, La Mirada, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California Filed July 24, 1968, Ser. No. 747,240 Int. Cl. Ellb 43/20, 43/22 U.S. Cl. 166-273 11 Claims ABSTRACT OF THE DISCLOSURE A process for recovering oil from porous subterranean reservoirs in which a bank of foam is established in the reservoir and displaced through the reservoir toward a spaced production well by the injection of a combination of gaseous and aqueous liquid drive fluids injected in the proportion of about 5 to 15 volumes of gas per volume of aqueous liquid as measured at reservoir conditions of temperature and pressure. Oil and other produced fluids are recovered from the production well. The drive fluid can be injected in the form of successive alternate slugs of gas and liquid, or the gas and aqueous liquid can be simultaneously injected into the reservoir. The gas remains in the gaseous state under reservoir conditions,

This invention relates to the recovery of oil from subterranean reservoirs and more particularly concerns an improved foam drive process for recovering oil from porous reservoirs.

It has long been recognized that substantial amounts of oil remain unrecovered at the completion of normal primary recovery operations. In orde1 to improve the recovery o-f oil, it has been proposed to supplement the native reservoir energy by the injection of various fluids to displace oil from the reservoir to a production well. It is known that the areal efficiencies and oil displacement efficiencies can be improved by flooding the reservoir with foam, or by injecting a bank of foam ahead of a conventional drive fluid. In one mode of operation, it is proposed that foam be generated at the surface by intimately contacting an aqueous solution of foaming agent with a gas. The resulting foam is injected into the oil-bearing reservo-ir through an injection well in communication with the productive Zones. However, this mode of operation has not been commercially successful because of the difliculty encountered in injecting foam into the porous formation and in displacing or driving the injected foam through the formation.

In another mode of operation, it is proposed that the foaming agent, or an aqueous solution of the foaming agent, be injected into the formation and followed by a gas drive. Foam is formed within the interstitial passages of the porous reservoir rock by the injected gas contacting the previously injected foaming agent. Ideally, gas inreservoirs in which foam is utilized to displace oil through the formation. In order to carry out a foam flood, it is necessary to transport the foaming agent from the injection well to the producing well. However, it has been found that although foam can be effectively formed in this manner, it is not readily transported over long distances by gas drive. Therefore, need exists for a method of forming a foam bank in a porous oil reservoir and for moving the foam bank through the reservoir to displace oil toward a spaced production well.

Accordingly, a primary object of the present invention ice is to provide a method for recovering oil from porous oil-bearing reservoirs. Another object of the invention is to provide a method for recovering oil from porous reservoirs in which foam is utiilzed to displace oil through the reservoir to a production well. A further object of the invention is to provide an effective method for transporting a foam 'bank through an oil reservoir whereby oil is displaced from the reservoir to a production Well. These and other objects of the invention will be apparent from the following detailed description of the invention.

Briefly, this invention contemplates a foam-drive process for recovering oil from porous subterranean reservoirs in which a bank of foam is established in the reservoir and displaced through the reservoir toward a spaced production well by the injection of a combination of gaseous and aqueous liquid drive fluids injected in the proportion of about 5 to l5 volumes of gas per volume of aqueous liquid. Oil and other produced fluids are recovered from the production well. The drive fluid can be injected in the form of successive alternate slugs of gas and liquid, or the gas and aqueous liquid can be simultaneously injected into the reservoir. The foam bank is effectively transported through the formation by the critical combination of gas and aqueous liquid drive fluids, thereby effecting a maximum recovery of oil.

The foam bank can be established in the reservoir by contacting at the surface an aqueous solution of a surface active agent capable of promoting the formation of stable foam with gas and thereafter conducting the foam through an injection well to the oil-bearing zone under sufficient pressure to force the foam into the porous formation. However, the foam bank is more preferably established in the reservoir by injecting a quantity of surface active foaming agent, or an aqueous solution of the foaming agent, into the reservoir, and thereafter injecting gas in an amount suflicient to cause the formation of foam within the interstitial passages of the porous formation on its contacting the foaming agent, or foaming agent solution therein.

Any water-soluble surface active agent can be employed that is capable of promoting the formation of a stable foam when contacted in aqueous solution by a gas. An example of a suitable water-soluble surfactant is polyoxyethylated octylphenol known commercially under the trademark Triton X-lOO. Other examples of suitable foam producing agents include dimethyl didodecenyl ammonium chloride, methyl trioctenyl ammonium iodide, trimethyl decenyl ammonium chloride, dibutyl dihexadecnyl ammonium chloride, and water-soluble salts of esters of C3-C6 sulfo dicarboxylic acids having the general formula o-(o)-OR MSOa-Cllnlzn-i (Il-(o)-OR where M is a substituent forming a water-soluble salt, such as alkali metals, ammonium, and substituted ammonium, R is C3-C6 alkyl substitutent, and n is an integer from 1-4, e.g., monosodium dioctyl sulfosuccinate, ammonium dilauryl sulfosuccinate, monosodium dibutyl sebacate, monosodium diamyl sulfoadipate, and others; and water-soluble peruoroalkanoic acid and salts having 324 carbon atoms per molecule, e.g., periluoro-octanoic acid, perfluoropropanoic acid, peruorononanoic acid.

Typical of other surface active agents which may be used in the practice of this invention are:

Chemical name Ethanolated alkyl guanidineamine complex.

Isopropyl naphthalene sodium Trademark:

Aerosol C-61 Aerosol OS sulfonate. Aerosol OT Diocetyl sodium sulfosuccinate.

Dicoco dimethyl ammonium Arquad 2C chloride Tallow trimethyl ammonium Arquad T chloride.

Fatty alcohol alkylolamine Duponol EP sulfate.

Modified ether alcohol sulfate Duponol RA sodium salt.

Duponol WAQ Sodium lauryl alcohol sulfate.

Condensation of hydrogenated tallow amide and ethylene oxide.

Modified fatty alkylolamide.

Ethylene cyclomido 1lauryl,

Z-hydroxy ethylene sodium al- Ethomid HT-60 Hyonic FA-75 Miranol HM coholate, methylene sodium concentrate carboxylate.

Same as Miranol HM except Miranol MM myristyl group is substituted concentrate for lauryl group. Nacconal NR Alkyl aryl sulfonate. Ninol AA62 Lauric diethanolamide. Ninol 1001 Fatty acid alkanolamide. Petrowet R Sodium alkyl sulfonate.

Condensation product of ethylene Pluronic L44 oxide with propylene glycol Product BCO C-cetyl betaine.

Polyoxyethylene alkyl Renex 650 aryl ether.

Sodium alkyl naphthalene Sorbit AC sulfonate.

Sodium salt of fatty alcohols, Sulfanole FAC sulfated.

Modified phthalic glycerol Triton B-1956 alkyl resin.

lsocytyl phenyl polyethoxy Triton X-45 ethanol.

Preferably, the surfactants utilized in this invention are those which form a stable foam in the presence of crude oil, and in reservoirs where the interstitial water contains a high concentration of salt, a surfactant is used which foams readily in the presence of oil and brine. A preferred surfactant found particularly useful in promoting the formation of foam in oil-bearing reservoirs is a surface active composition marketed by Procter & Gamble Company under the trademark O.K. Liquid and described in U.S. Pats. Nos. 2,941,950 and 3,330,346. Another preferred surface active agent for promoting the formation of foam in oil-bearing reservoirs is an alkyl polyethylene oxide sulfate composition marketed by General Aniline and Film Corporation under the trademark Alipol CD-128 filed Oct. 3, 1967.

While many of the surfactants utilized in accordance with the invention may be injected into the formation by themselves, it is preferred that they be utilized in the form of aqueous solutions. Therefore, it should be understood that many surfactants which are primarily oil-soluble nevertheless have suicient Water solubility to permit their use in aqueous solutions, and have the ability to form tenacious foams under reservoir temperatures and pressures.

The concentration of surfactant in the aqueous solution employed in accordance with this invention will depend in large part on the particular agent utilized and the type of formation which is to be produced. For instance, where a particular type of formation creates a condition under which much of the surfactant is adsorbed in the interstices of the formation, it will be necessary to employ a greater amount of surfactant so that suicient surfactant will remain to form a foam bank within the rservoir on the subsequent injection of a gas. Surfactant concentrations between about 0.01 to 10 Weight percent of the solution in which they are incorporated are generally suitable for purposes of the invention with the preferable concentration being about 0.1 to 1.0 weight percent.

The quantity of surfactant vehicle or carrier will depend largely upon such well recognized factors as the recovery pattern, spacing between wells, the porosity of the formation, and the thickness of the formation. Ideally the quantity of vehicle or carrier employed should be such that a sufficient amount of liquid is available to completely foam the surfactant solution upon the intimate contact of the solution with the gas. Since the amount of solution required to accomplish this cannot be precisely determined in advance, the most convenient method for expressing the quantity of surfactant solution to be used is in terms of reservoir pore volume. In general, from about .01 to 0.3 pore volume of solution will be utilized with the preferred range being about 0.05 to 0.10 pore volume. Quantities in the upper part of this range may be required for operations in which relatively dilute solutions are employed or in which surfactants having an affinity to absorb upon the rock to a relatively high degree are used. Lesser quantities may be utilized where the surfactant employed is a highly effective one and where the concentration of the solution is high.

Following the injection of the foam, or in the preferred embodiment wherein foaming agent or a solution of foaming agent is injected into the formation, there is injected a combination of gaseous and aqueous liquid drive uids maintained in the proportion of about 5 to 15 volumes of gas (measured at reservoir conditions of temperature and pressure) per volume of aqueous liquid injected into the formation. The gasiform driving fluid is selected so that it will remain a gas at both injection conditions and under conditions encountered in the rservoir. Suitable gases include natural gas, methane, ethane, nitrogen, air, carbon dioxide, engine exhaust gases, mixtures of these gases, and other similar gases. The aqueous liquid drive fluid can be water or brine and the like. The combined gaseous and aqueous liquid drive fluids can be injected in alternating slugs of gas and liquid, or the fluids can be simultaneously injected in the form of a gas-liquid mixture, so long as the critical ratio of gas to aqueous liquid is maintained.

Thus, in one embodiment of the invention, the foaming agent, or foaming agent solution, is followed by the injection of successive alternating slugs of gas and liquid until the desired recovery of oil is attained, as usually indicated by the producing water/oil ratios becoming excessive. It is preferred that the aqueous liquid be injected in slugs of about 0.01 to 0.1 pore volume and that the amount of gas injected in each slug be controlled to maintain the gas/water ratio between about 5 to 15 Volumes of gas per volume of liquid.

ln another embodiment of the invention, the foaming agent, or foaming agent solution, is followed by the injection of a mixture of drive gas and aqueous liquid drive fluid injected in the proportions of between about and volumes of gas per volume of aqueous liquid. In this embodiment, gaseous drive fluid and aqueous liquid drive fluid are simultaneously injected through an injection well and into the reservoir to displace oil and other fluids towards a spaced production well. These fluids are recovered from the production well in conventional manner.

Thus, in the embodiments of this invention wherein the gaseous and aqueous liquid drive fluids are injected either successively or as alternate slugs, it is preferred that the ratio of gas to liquid injected be controlled in the ratio of about 5/1 to 15/1.

In carrying out the process of the invention, the surfactant or surfactant solution is first injected into the reservoir through one or more injection wells arranged in a logically spaced pattern. Five spot, seven spot, line drive, or other conventional well patterns may be ,utilized and generally are preferable. After a sufficient amount of surfactant to effect the formation of a tenacious foam bank within the formation has been introduced, a gaseous drive fluid or a mixture of a gasiform fluid and an aqueous liquid are injected to displace the surfactant into the reservoir, and to form a bank of foam therein. The driving fluid will consist of the injection of alternate slugs of gas and aqueous liquid, or a mixture of gas and aqueous liquid simultaneously injected into the reservoir. In either case, the volume of gas and liquid injected is controlled to maintain the proportion of the gaseous and liquid drive fluid within the range of about 5 to 15 volumes of gas per volume of liquid injected. Upon the introduction of the gas, the gas will tend to channel through the formation until it reaches the surfactant or surfactant solution at which time a tenacious foam bank is formed within the interstices of the formation. Gas injection will be somewhat restricted until injection of the aqueous liquid is commenced, whereupon the foam bank will move through the reservoir toward the open producing wells thereby displacing formation fluids, such as connate water and petroleum oil, before it, and will also confine the driving fluid within a relatively finite area. Although the recovery operation can be discontinued at any time, gas and aqueous liquid injection is conventionally continued until the fluids produced from the production well have a relatively low oil content thereby indicating that further recovery of petroleum oil from the subterranean formation is uneconomical.

In still another embodiment of this invention, after the initial surfactant or surfactant-containing solution has been injected into the reservoir, a substantially surfactantfree, non-gaseous displacing liquid is injected through the injection well and into the formation in an amount sufficient to displace the initially injected surfactant or surfactant solution outwardly into the formation a distance of about l0 to 50 feet from the well. Thereafter, alternate slugs of gas and aqueous liquid or mixtures of gas and aqueous liquid driving fluid are injected to form a bank of foam in the reservoir and to move the foam bank through the reservoir. Displacement of the surfactant outwardly into the reservoir prior to injecting gas prevents the formation of any substantial quantity of foam immediately adjacent to the well that will restrict injection of the subsequently injected drive fluids.

By the formation of foam within the reservoir preceding the principal drive fluid, and driving the foam through the reservoir with a combined gaseous and aqueous liquid drive fluid, additional oil is recovered because the generated foam is more effectively moved through the formation and tends to invade the larger capillaries or interstices of the formation, thereby diverting the remainder of the foam and drive fluid into the smaller interstices or capillaries. In addition, a foam bank provides a more favorable drive fluid mobility ratio, improves conformance and displacement efficiency, and results in more complete displacement of oil from the reservoir.

The invention is further described by the following examples which are illustrative of specific modes of practicing the invention and are not intended as limiting the scope of the invention as defined by the appended claims.

EXAMPLE 1 The effectiveness of a combined gas/water drive in transporting foaming agent through porous earth formations is illustrated by the following test. A number of substantially identical sand packs are prepared to simulate cores of an earth formation and saturated with water.

The poor foam transport property of gas is illustrated by injecting a 0.1 pore volume slug of aqueous foaming agent solution into one of the water saturated cores and then passing nitrogen gas through the sand pack to form foam therein and to drive the foam through the core. Liquid displaced from the core is collected and analyzed for the presence of foaming agent. No foaming agent is detected in the effluent liquid, even after pore volumes of gas is passed through the core.

This test is repeated on other of the water saturated cores by driving the foam with alternate slugs of gas and water maintained at various volumetric gas/water ratios. The maximum concentration of foaming agent in the effluent liquid occurs after the injection of only 10 pore volumes of gas at a gas/water ratio of 10/1. Results of these tests are summarized in Table I and illustrated graphically in FIG. 1 which is a plot of the Foaming Agent Concentration of the Eflluent Liquid (expressed as a percentage of the concentration of foaming agent in the injected solution) vs. Drive Fluid Gas/Water Ratio.

TABLE I Foaming agent concentration 1 Gas/ water Gas/water Gas/water ratio 10/1 rat1o 100/l ratio 100G/l Pore volumes gas, percent .HMH OUDBWOOOOOOOOOOOO 1Percent of initial concentration.

It is apparent from the foregoing that combined gas and water drive fluids in the proportion of 10 volumes of gas per volume of water transport foaming agent through a porous structure much more efficiently than either gas alone or combined gas and water drives at higher gas/water ratios.

EXAMPLE 2 The oil recovery efficiencies of a number of fluid drives are compared in the following tests. A Boise sandstone core 8 feet long is initially saturated with 67.5% crude oil and 32.5% water and then water flooded in conventional manner. The oil displaced from the core is collected and measured. Water flooding to residual oil saturation recovered about 55.5 percent of the oil.

The core was resaturated with crude oil and a second test made by injecting 0.1 pore volume of 1% aqueous foaming agent solution into the core and then injecting gas to form foam and to drive oil from the core. Several additional foam floods are performed using alternate slugs of gas and water as drive'fluid, 0.1 pore volume of water being injected in each slug and the gas being injected in the amounts of 5, l0, 15 and l0() volumes of gas, respectively, per volume of water. Oil recoveries are determined.

ment which comprises employing as the drive uid a combination of a gas that remains in the gaseous state under reservoir conditions and aqueous liquid in the proportion of between about to 15 volumes of gas per volume of The results of the foregoing tests are reported in Table 5 liquid as measured at reservoir conditions of temperature 2 and illustrated graphically in FIG. 2 which is a plot and pressure. of the percent oil recovery vs. drive fluid gas/water 2. The method defined in claim 1 wherein foam is ratio. It should be noted that the points for 0 gas/ generated at the surface and injected into the reservoir Water ratio and infinite gas water ratio, are plotted through the injection well to establish therein said bank at the extreme ends of the abscissa. of foam.

TABLE 2 Test No. 1 2 3 4 5 e Displacement type Water Foam Foam Foam Foam Foam nood. flood. flood. flood. flood. flood. Drive fluid Water- Gas Gas and Gas and Gas and Gas and water. water. water Water Gas/water ratio 0 00 100/1 15/1 10/1 Oil recovery, percentl 55.5 57.0 600 64.0 64.4

l Percent of oil-in-plaee initially.

These tests demonstrated that a foam flood recovers 3. The method dened in claim 1 wherein said foam more oil than a water ood and that maximum oil rebank is established by injecting a foaming agent into covery is obtained with a foam flood displaced by gas the reservoir through the injection well, and thereafter and water in the proportion of about l() volumes of gas injecting gas whereby foam is formed in said reservoir per Volume of water. on contact with said foaming agent.

EXAMPLE 3 25 4. The method defined in claim 1 wherein said gas is selected from the group cons1st1ng of natural gas, meth- A COmmCrCal Scale foam OOd iS COIldllCed Using the ane, ethane, nitrogen, air, carbon dioxide, engine exhaust improved drive fluid of this invention. The flood is cargases, and mixtures of said gases. ried out on an oil sand depleted to economic limits by 5 The method defined in claim 1 wherein said aqueous conventional primary recovery. A conventional five-spot liquid is selected from the group consisting of water and pattern is employed with four injection wells located in a brine, square pattern and a single producing well located at 6, A method for recovering petroleum from a subthe center. terranean reservoir penetrated by an injection Well and a The iiood is initiated by injecting 0.05 pore volume production well spaced apart in the reservoir, which comof an aqueous solution containing 1 percent by Weight prises; of water-soluble foaming agent, Next, water is injected injecting through said injection well and into said reserto displace the foaming agent solution outwardly into the voir between about 0.1 to 0.3 pore volume of an formation a distance of about 20 feet. Then alternate aqueous solution comprised of water and between slugs of natural gas and Water are injected. The water about 0.01 to 10.0 weight percent of a foaming slugs amount to about 0.1 pore volume and the gaseous agent; slugs to about 1.0 pore volumes each. Oil is recovered thereafter simultaneously injecting through said injecfrom the central producing well. tion `Well and into said reservoir a gas that lremains EXAMPLE 4 in the gaseous st ate under reservoir conditions and an aqueous liquid, sa1d gas belng lnjected 1n the Another embodiment 0f the imprOVed foam flOOd Of 45 amount of about 5 to 15 volumes per volume of said this invention is employed in a commercial scale foam aqueous liquid as measured at reservoir conditions flood. This flood is carried out on an oil sand depleted to of temperature and pressure; and economic limits by conventional primary TCCOVSTY and recovering petroleum from said production well. then by water ooding. A line drive ooding pattern is 7, The method defined in claim 6 wherein said gas is employed in which the injection Wells are arranged in a selected from the group consisting of natural gas, methsubstantially straight line and a plurality of producing ane, ethane, nitrogen, air, carbon dioxide, engine exhaust wells are arranged in another parallel line spaced apart gases, and mixtures of said gases. from the injection wells. 8. A method for recovering petroleum from a sub- The foam flood is initiated by injecting 0.1 pore volume terranean reservoir penetrated by an injection well and a of an aqueous solution containing 2 weight percent of a 55 production well spaced apart in the reservoir, which comwater-soluble foaming agent. This solution is caused to prises: foam in the reservoir and is displaced through the reserinjecting through said injection well and into said voir by simultaneously injecting internal combustion enreservoir between about 0.01 to 0.3 pore Volume gine exhaust gas and water in the proportions of about 5 of an aqueous solution comprised of Water and bevolumes of gas per volume of Water. Oil and other fluids tween about 0.01 to 10.0 weight percent of a foamare recovered from the injection wells. Drive fluid injecing agent; tion is continued until the producing water/oil ratios inthereafter injecting through said injection well and into crease to an uneconomical limit. said reservoir alternate slugs of a gas that is sub- Various embodiments and modications of this invenstantially uncondensed at reservoir conditions and tion have been described in the foregoing description and an aqueous liquid, said gas being injected in the examples, and further modification will be apparent to amount of 5 to l5 volumes of gas per volume of those skilled in the art. Such modifications are included aqueous liquid as measured as reservoir conditions within the scope of this invention as defined by the folof temperature and pressure; and lowing claims: recovering petroleum from said injection well.

Having now described the invention, I claim: 9. The method defined in claim 8 wherein said gas is 1. In the method for recovering petroleum from porous selected from the group consisting of natural gas, methsubterranean reservoirs wherein a bank of foam is estabane ethane, nitrogen, air, carbon dioxide, engine exhaust lished in the reservoir and thereafter displaced through gases, and mixtures of said gases. the reservoirs towards a production Well by means of a 10. The method dened in claim `8 wherein said slugs drive fluid injectedthrough an injection well, and petroof aqueous liquid are injected in an amount between leum is recovered from the production Well, the improveabout 0.01 to 0.1 pore volume.

9 11. The ymethod dened in claim 8 wherein a slug of substantially surfactant-free aqueous liquid is injected into the reservoir following the injection of said foaming agent solution to displace said solution into the reservoir a distance from said well prior to the injection of said gas.

References Cited UNITED STATES PATENTS 2,866,507 12/19'58 Bond et al. 166-9 2,875,833 3/1959 Martin 166--9 10 3,249,157 5/ 1966 Brigham et al 166-9 10 OBrien et al. 166--9 Bond et al 166--9 Bernard et al. 166-9 Bond et al. 166-9 Quance 166-9 U.S. Cl. X.R. 

